Mercerized wood-fiber tissue and process of preparing same



Patented 4, 1930 This invention relates to the preparation 4 of materialadapted for conversion 1nto pure or high grade cellulose derivatives,andv is more especially concerned with the prepara-" 5 tion ofcellulosicfiberadapted for conversion into the lower nitrocelluloses, such asthose customarily employed for the manufacture of artificial silk,films, lacquers, and kindred products.

Although the process herein to be described may be practised withcellulosic fiber of various kinds, it is applicable most expediently topaper or-tissue prepared from wood pulp, particularly one containing ahigh percentage of alpha or resistant cellulose. 1 Such high alphacellulose fiber, which for convenience of designation will herein-'aftei' be termed alpha fiber, may be con- 1 verted into cellulosederivatives having '20 physical and chemical properties compara- 'ble toderivatives prepared fromv cotton fiber or cotton linters, in contrastto the relative- Lly impure derivatives having inferior. prop erties,prepared from chemical wood fiber of lower alpha cellulose content. Suchalpha fiber may beproduced as described inv application for patent,Serial No. 72,522, filed December 1, 1925, by George A. Richter andMilton 0. Schur, by treating a pulp, e. g.,

the usual-commercial sulphite pulp conta1ning, say, about 85% to 8 7%alpha cellulose, in a solutionof caustic soda or equivalent alkalinecompounds under the appropriate conditions of time, temperature,and'chem -'35 real concentratlon.

lulose contentofithe fiber, viz, beta and gamma celluloses, ligneous andother coloring material, is dissolved, so that there is 40, produced afiber containing upward of 93% a1 ha cellulose and which requires only arel ativel small amount of bleach for conversion into /fiber of highwhiteness, and is usable as anew rag or cotton fiber substitute in themanufacture of high gradev writing papers and in the preparation ofcellulose derivatives of high commercial value and purity. Sometimes itis desirable to treat the pulp, prior to the alkaline treatment, with aBy such treatment, a I considerable portion bf-the non-alpha cel- PATENTOFFICE 0P BERLIN, NEW HAMPSHIRE, Assrenons HAMPSHIRE, A CORPORATION orMAINE AND PROCESS or PREPARING SAME v 5, 1927. Serial No. 159,235.

When alpha fiber of very high alpha cellulose content, about 95% to 98%,is desired, the initial alkaline treatment, is succeededby asecondfalkaline treatment, as described in application for patent,Serial No. 75,888, filed December 16, 1925, by George A. Richter. Suchdouble alkaline treatment not only further reduces the quantity ofbleach required to whiten the fiber, but produces fiber whichconstitutes an excellent raw material for the preparation of high gradecellulose derivatives. t 1

In application, Serial N o.-140,676, filed October 9, 1926, by GeorgeA.-Richter, Milton 0. Schur,-and Royal I-L Rasch, the advantages ofmercerizing cellulose fiber, and more particularly alpha fiber, prior toconversion into cellulose derivatives, especially the lowernitrocelluloses, are disclosed, and, in our application, Serial No.140,675, filed October 9, 1926, the advantages of'mercerizing paper ortissue formed from such fiber preferably beaten, and a subsequenttreatment with hot alkaline water, are disclosed. I

We have now discovered that the addition of a relatively small amount ofan oxidizing or bleaching agent, e. g.., hypochlorite 'or permanganate,to the 'mercerizing solution ita nt additional removal of undesirablecolor ing matter and yields a fiber which is convertible into cellulosederivatives or cellulose products, such as rayon, films, lacquers, etc.,of colorlessness or freedom from color practically equal to likederivatives or cellulose products prepared from good cotton fiber.

and/or to the hot water, efl:'ects an imporfin The use of a small amountof oxidant t0 remove coloringmaterial from the alpha fiber" while suchfiber isbeing treated with a strongly alkaline solution is believeditobe distinctly advantageous, for thetremendous OH ion concentration insolution, we believe,

represses substantially entirely a tendency toward the oxidation of thealpha or resistant 0 1 halogenizmg or. an oxidizing solution, e. g.,\cellulose content of the fiber, while permitting 100 celluloseproducts.

. the use of which mercerizlng strength and stretch a deep brown color,

borne out by the fact that the treatment has substantially no effectupon the excellent nitrating yield, low acid retention, and high 'offilaments and films prepared from the mercerized fiber. The nitratedfiber may yield solutions pf slightly lower viscosity than usual, butthis is advantageous for the preparation of many nitro- In carrying outone mode of procedure, the alpha fiber, preferably in tissue form andbeaten more or less, is treated by steeping it in a caustic sodasolution of mer'cerizing strength and containing the oxidizin agent,until the desired mercerization of the 'ber has or treated with water,preferably hot water,

latter effects a further purification of the fiber. The hot waterpreserves the tissue in a firm, integral condition, whereas cold wateris likely to cause the disintegration ofrthe tissue into a pulpy masswhich is diflicult to handle Theme of hot water after the mercerizingtreatment, as indicated, is therefore a step of paramount importance,as'it makes possible the practice of a continuous and economicalprocess. Should'the solution contain no oxidizing agent, as heretofore,the hot water assumes the depth of color depending upon the purity oralpha cellulose content of the alpha fiber. When the mercerizingsolution contains anoxidizing agent as in accordance with the presentinvention, however, the hot water is of much lighter color andfrequently is colorless, as the tissue retains suflicient oxidant afterthe mercerizing treatment to oxidize or to bleach coloring matterextracted from or generated in the fiber by the hot, dilute caustic sodasolution formed with the hot water. water treatment, the tissueisneutralized of residual caustic soda by a steeping in an acid or souringsolutionwhich-preferably contains an acid reducing agent, which, inaddition to neutralizing the free caustic soda, neutralizes or reducesthe last traces of freeoxidant. If'desired, of a mixture ofaan acid anda reducing compound ma expedient to use a single compound to effect boththe neutralizing and reducing actions. Thus, for example, sodium h-yochlorite may be used as the oxidant in t e mercerizing solution, andsulphurous acid may be used in the souring. solution as the acidreducing agent. After the souring, the tissue is washed free fromneutralized products with cold water, and finally is dried. The tissuetends to crinkle, upondrying, so that if the tension usually appliedduring drying when the material is in continuous sheet form is reduceddrowned mercerizing solution.

After the hot course, a solution containing. dergo crinkling, be used,but 1t 1s usually more or removed, there results a crinkled tissue. Suchcrinkled tissue may be cut up into small pieces, which when nitratedhave but little tendency to stick together'in the nitrating bath or inthe centrifuge.

A specific example of procedure which may be practised and which hasbeen found to give excellent results, may be substantially as follows.The alpha fiber is sheet or nitrating tissue, preferably below 20preferably treated in the form of a continuous thin waterleaf" pounds inbasis welght (480-2 LX36), or

equivalent to a thickness of approximately .003 inches. The fiber ispreferably beaten prior to formation into the tissue, as a beaten fiberhas proven to give better results upon nitration than an unbeaten fiber.The tissue is passed through or immersed in a caustic soda solutioncontaining about 19% NaOH and about 0.3% available chlorine (based onsolution), at about 68 F., the time of immersion being from about two toten seconds. Under these conditions, we not only realize more effectiveremoval and color-generating substances, i. e., substances causingcoloration in nitrocellulose products such as lacquers, films, etc., butwe retain all the advantages accruing from mercerization. The tissue isthen preferably passed between squeeze rolls, which serve to expresstherefrom excess solution for reuse in mercerfization. The tissue 5 sthen treated with water, preferably by passing it through acountercurrent flowing stream of hot water at or near the boiling point.The concentrated caustic soda solution retained by the tissue forms withthe hot water a dilute caustic soda solution which effects a furtherremoval or extraction of those impurities unaflected by the relativelcold, concentrated ince suflicient oxi dant is retained by the tissue tobleach any coloring material extracted from or generated in-the fiber,the hot alkaline water is light colored and frequently colorless. Thetissue is then passed through a 0.15% to 0.25% sulphurous acid solutionat room temperature, and then washed with sufiicient cold water toremove the reaction products. 7 The neutral tissue is then dried, eitherunder ten sion or under conditions permitting it to unwhich may bepreferable, as the crinkled tissue when out up into small pieces andnitrated has but little tendency to stick together in the nitrating bathor in the centrifuge. v

By our process, two ver important ends are simultaneously attaine as inour application hereinbefore identified, .viz, the apha fiber ismercerized or chemically hydrated, and it is simultaneously purified orrefined.

It should be understood that our process is its more compact condition,g ves a higher unbeaten. With tissue, however, certain practicaladvantages are to benoted, to wit:

r tively (a) Uniformity of treatment is easier to attain, as all thefibersIare more easily accessible to the reagents applied.

(b) The apparatus necessary is comparasimple and inexpensive.

(0 Continuous operation is more easily realized. e i (d) The dried,processed tissue, because of yield of nitrocellulose, and has a loweracid retention.

Again, while inthe example given certain definite-conditions ofprocessing have been specified which have yielded excellent results,nevertheless, we desire to have it understood that the temperature andcomposition of mercerizing solution, and the time of treatment with'suchsolution,'may be varied within rather wide limits.

The tissue may be steeped in the mercerizing solution immediately aftersheeting and partial or comple'tejdrying, or after sheeting on the wetend ofa Fourdrinier or cylinder paper-ma king machine and passingthrough press. rolls but without drying. A partial or completeconservation of the steam usually expended in drying the tissue may thusbe realized, when desired, bythe latter ,method. When a damp or wettissue is to be mercerized, it is advantageous to employ astrongersolution than otherwise, so as to attain the necessary rate of diffusioninto and through .50, before the bleaching zone-in the countercur:

rent streannaoiji hot water is reached. The

the tissue to produce the 'desired merceri zation, but withoilt causinga disintegration or falling apart of thetissue into fragments or intopulp.

If desired, we may also add a very small amount of oxidant to thecountercurrent flowing stream of hot water at any suitable point, 1preferably midway between its influent and efiluent ends. Of course,should we so desire,

we might omit the addition of oxidant to the mercerizing solution, andadd the appropriate amount of oxidant to the countercurrent stream ofhot water only. Less oxidant need be added here than to the mercerizingsolution, because some of the coloring matter, is independently removedby thehot water eflectivenessbf removing coloring material is notlessened, even though the tissue first contacts with eflluent coloredhot water, because any residual coloring matter in the tissue aftermercerization, and/orcoloring materialo'ador absorbed thereby from theeflluent hot water, are gradually removed as the tissue proceeds throughthe bleaching zone in-the countercurrent flowing stream. Suchremoval ofcoloring is evidenced by a gradual lightening of the color of the waterstream;

. toward the influent end of the countercurrent dant, washing the webaration of nitrocellulose and other cellulose derivatives substantiallyfree from coloring matter and from which colorless-filaments,

films, and congeneric products .may be produced. Inasmuch as the absenceof coloring matter in nitrocelluloses andother cellulose derivativesprepared from good cotton fiber has in the past been one of theoutstanding advantages of cotton'as a raw material, and, again, inasmuchas the product of the present inventionmay be manufactured at a unitcost below that ofcotton and its characteristics closely controlled ordefinitely varied, it is preeminently satisfactory as a pure celluloseraw material.

While the advantages of the present invention have been described indetail in connection with the prepars'ztionof nitrocelluloses, and moreespecially the lower nitrocelluloses,

v it is to be noted, as previously adverted, that advantages are gainedin the preparation of other cellulose derivatives. Thus, in thepreparation of cellulose acetate, smoothness of acetylation and qualityof cellulose acetate are improved, particularly with regard to theelimination of undesirable color.

We claim:

1. A process which comprises treating a high alpha cellulose fiber witha caustic soda solution of mercerizing strength containing a smallamount of an oxidizing agent, substantially completely removing thetreating chemicals from the fiber, and converting the fiber into acellulose derivative.

2. A process which comprises treating. a

,high alpha cellulose wood fiber with a caustic soda solution ofmercerizing strength containing. an oxidant, washing the treating fiber,neutralizing'the lasttraces of caustic soda and oxidant, and washing thefiber free from reaction products. r

3. A process which comprises treating a high-alpha-cellulose-containing-wood fiber witha caustic soda solution of mercerizing strengthcontainin'ga small amount of an oxidant, washing the treated fiber,neutralizing the last traces of caustic soda and oxidant, washing thefiber free from reaction products, and nitrating the fiber.

4. That. step which comprises treating a wood fiber web with a causticsoda solution ofmercerizing strength containing anoxi- 7 substantiallyfree from treating chemicals, and converting into a cellulosederivative.

5. A process which comprises treating a high alpha cellulose wood-fibertissue with a caustic soda solution of mercerizing strength containingan oxidizing agent, and treating the tissue with hot water.

6. A process which comprises treating a high alpha cellulose wood-fibertissue with a caustic soda solution of mercerizing strength containingan oxidizing agent, squeezing excess solution from the tissue, andpassing the treated tissue through a'countercurrnt flowing stream of hotwater.

7. A process which comprises treating a high alpha cellulose wood-fibertissue with a caustic soda solution of mercerizing strength containingan oxidizing agent, passing the treated tissue through a'countercurrentflowing stream of hot water,- and adding an oxidizing agent to thestream of water.

8. A continuous process which comprises successively passing acontinuous sheet of high alpha cellulose fiber through a caustic sodasolution of mercerizing "strength and through a countercurrent flowingstream of hot water containing an oxidizing agent;

9. A process which comprises treating a high alpha cellulose wood-fibertissue with a caustic soda solution of passingthe treated tissue througha countercurrent flowing stream ofhotwater, and adding an oxidizingagent to the stream of water.

10. A process which comprises treating a high alpha cellulose wood-fibertissue with a caustic soda solution ofmercerizing strength containing anoxidant, treating the tissue with hot water, neutralizing caustic sodaand oxidant remaining in the tissue, and washing the tissue free fromreaction prod ucts.

, 11. A continuous process which comprises successively passing acontinuous. sheet of high alpha cellulose fiber through a caustic sodasolution of mercerizing strength containing an oxidant, through acountercurrent flowing stream of tralizing solution, and through washwater.

12. A process which comprises treating a high alpha cellulose wood-fibertissue with a containing an oxidant, treating the tissue mercerizingstrength,

hot water, through a neusignatures. caustic soda solution of mercerizingstrength I 14. A process which comprises treatin a.

high alpha cellulose wood-fiber tissue wit a caustic soda solution ofmercerizing strength containing an oxidant, treating the tissue with hotwater, neutralizing caustic soda and oxidant remaining in the tissue,washing the tissue free from reaction products, drying the tissue underconditions permitting it tocrinkle, and nitrating the crinkled tissue.

15. A process which comprises treating a high alpha cellulose wood-fibertissue in a caustic soda solution of mercerizing strength containing anoxidant, substantially completely removing the treating chemicals fromthe tissue, and converting the tissue into a cellulose derivative.

16. A mercerized, high alpha cellulose wood-fiber tissue suificientlyfree from non-. alpha' cellulose ,components including beta and gammacellulose, ligneous, and other coloring material to be convertible intolower nitrocelluloses of colorlessness or freedom prepared from goodcotton fiber.

17. A process which comprises treating cellulose fiber with amercerizing solution containing an oxidant, washing the treated fibersubstantially free from chemicals, and converting the washed fiber intoa cellulose derivative. a

18. A process which comprises treating a from color practically equal tonitrocelluloses cellulose fiber tissue with a mercerizing solutioncontaining an oxidant, and washing the tissue substantially free fromchemicals in hot water. i f

19. A process which comprises treating cellulose fiber tissue withamercerizing solution containing an oxidant, washing the tissuesubstantially free from chemicals inhot water, and converting the washedtissue into a cellulose derivative.

20. A cellulose fiber tissue with a mercerizing solution containing anoxidant, treating the tissue with hot water, drying the tissue underconditions permitting it to crinkle, and conyerting the crinkled tissueinto a cellulose derivative.

In testimony whereof we have afiixed our MILTON 0. serum. ROYAL H.RAYSCH.

with hot water, neutralizing caustic soda and V oxidant remaining in thetissue, washing the 55 tissue free from reaction products, and dryingthe tissue.

13. A process which-comprises treating a high alpha cellulose wood-fibertissue with a caustic soda solution of mercerizing strength contalningan oxidant, treating the tissue process which comprises treating a llO

